1. Field of the Invention
The present invention relates to a controller driver, a display device, and a control method therefor. In particular, the present invention relates to a controller driver incorporating a touch panel controller, a display device including a touch panel using the same, and a control method for the display device.
2. Description of Related Art
In recent years, products equipped with touch panels capable of inputting external information through a display screen have been developed in the field of mobile devices such as PDAs and cellular phones. FIG. 17 shows a schematic system configuration of a cellular phone according to a related art. As shown in FIG. 17, a display block 1 includes a display panel 10 and a touch panel 11, and a cellular phone main-body block 2 includes a CPU 20 and a touch panel controller 21. Note that if the display panel 10 is an LCD, a backlight is separately provided in the display block, and the backlight, the display panel, and the touch panel are stacked in this order.
The touch panel 11 is connected to the touch panel controller 21 through an FPC 13. The touch panel controller 21 controls the touch panel 11 based on a touch panel control signal, and acquires a touch panel signal when an external input is applied to the touch panel 11. The touch panel controller 21 converts the acquired touch panel signal into a position coordinate signal (Yt, Xt) and transfers the position coordinate signal to the CPU 20. The display panel 10 is connected to the CPU 20 through an FPC 12. The display panel 10 is driven by a controller driver 3. The controller driver 3 is controlled in accordance with image data Din and a control signal which are received from the CPU 20.
FIG. 18 shows the configuration of the controller driver 3 according to the related art. The controller driver 3 incorporates a display memory 31 in order to reduce power consumption. In the case of still image display, image data stored in the display memory 31 is read out and displayed, thereby reducing power consumption associated with the transfer of image data between the CPU 20 and the controller driver 3.
Meanwhile, when an external input is applied to the touch panel 11 as shown in FIG. 19, the CPU 20 needs to perform processing for generating a cursor data image based on the position coordinate signal (Yt, Xt) and for combining image data 1 and a cursor image which are currently displayed. The CPU 20 also needs to transfer the composite image data Din, which is obtained by combining the image data 1 and the cursor image, to the controller driver. This causes problems such as an increase in CPU processing load and an increase in power consumption.
In view of this, Japanese Unexamined Patent Application Publication No. 04-360191 (Ooya) proposes an input device in which a liquid crystal panel and a touch panel are stacked in this order on a display device in order to reduce the CPU processing load. In the input device disclosed by Ooya, a cursor is displayed on the liquid crystal panel based on touch position information from the touch panel. An operator can visually recognize an image displayed on the display device through the liquid crystal panel, and can also recognize the image and the cursor. This eliminates the need for the CPU to generate composite image data by combining the image data and the cursor image, which are to be displayed on the display device, even while the touch panel is being operated.